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Zachary W Davis-Gilbert, Xuelan Wen, Jason D Goodpaster, Ian A Tonks
A combined computational and experimental study on the mechanism of Ti-catalyzed formal [2+2+1] pyrrole synthesis from alkynes and aryl diazenes is reported. This reaction proceeds through a formally Ti(II)/Ti(IV) redox catalytic cycle as determined by natural bond orbital (NBO) and intrinsic bond orbital (IBO) analysis. Kinetic analysis of the reaction of internal alkynes with azobenzene reveals a complex equilibria involving Ti=NPh monomer/dimer equilibrium, Ti=NPh + alkyne [2+2] cycloaddition equilibrium, along with azobenzene and pyridine inhibition equilibria prior to rate determining 2nd alkyne insertion...
May 15, 2018: Journal of the American Chemical Society
Junyi Zhou, Haian Xu, Zaizai Tong, Yuhui Yang, Guohua Jiang
Herein, dual stimuli-responsive compound vesicles were constructed based on host-guest interaction between a water-soluble pillar[6]arene (WP6) and an amphiphilic azobenzene-containing block copolymers (BCP). Reversible morphological transformation between compound vesicles and solid aggregates was achieved by repeated pH- and photo-stimuli. These compound vesicles were then applied in the controlled release of water-soluble anticancer drug, doxorubicin hydrochloride (DOX · HCl). Upon external stimuli, the DOX · HCl displayed a faster release rate than that without stimuli...
August 1, 2018: Materials Science & Engineering. C, Materials for Biological Applications
Todd M Doran, Bradley L Nilsson
Alzheimer's disease (AD) is characterized by chronic neurodegeneration and the insidious accumulation of senile plaques comprised of the amyloid-β (Aβ) peptide. An important goal in AD research is to characterize the structural basis for how Aβ aggregates exert their noxious effects on neurons. We describe herein synthetic steps to incorporate a light-controlled β-turn mimetic, 3-(3-aminomethylphenylazo)-phenylacetic acid (AMPP), into the backbone of a putative turn region within Aβ. AMPP adopts a rigid β-hairpin turn when azobenzene is in the cis conformation, and can adopt an extended "β-arc" turn in the trans-azobenzene conformation...
2018: Methods in Molecular Biology
H A Schwartz, U Ruschewitz, L Heinke
Smart, molecularly structured materials with remote-controllable properties and functionalities attract particular attention and may enable advanced applications. In this respect, the embedment of stimuli-responsive molecules, such as azobenzenes, spiropyrans or diarylethenes, in metal-organic frameworks (MOFs) is a very fascinating approach, resulting in easily accessible photoswitchable, nanoporous hybrid materials. It is an attractive alternative to the incorporation of the smart moieties in the MOF scaffold, which usually demands complex synthetic efforts...
May 8, 2018: Photochemical & Photobiological Sciences
Gabrielle A Mandl, Paola A Rojas-Gutierrez, John A Capobianco
To circumvent the need for direct UV excitation in a supramolecular hydrogel composed of an azobenzene-modified poly(acrylic acid) copolymer and deoxycholate-β-cyclodextrin as a crosslinker, we modified this system for use with LiYF4:Tm3+/Yb3+ upconverting nanoparticles, which emit UV light upon NIR excitation. A complete gel-sol transition was observed in 60 minutes upon 980 nm irradiation. No change was observed under similar conditions of a control sample over the same period of time.
May 4, 2018: Chemical Communications: Chem Comm
Monalisa Goswami, Bas de Bruin
Azobenzenes are versatile compounds with a range of applications, including dyes and pigments, food additives, indicators, radical reaction initiators, molecular switches, etc. In this context, we report a general method for synthesizing o -aminoazobenzenes using the commercially available cobalt(II) tetraphenyl porphyrin [CoII (TPP)] . The net reaction is a formal dimerization of two phenyl azides with concomitant loss of two molecules of dinitrogen. The most commonly used methodology to synthesize azobenzenes is based on the initial diazotization of an aromatic primary amine at low temperatures, which then reacts with an electron rich aromatic nucleophile...
May 1, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Lorenzo Casimiro, Jessica Groppi, Massimo Baroncini, Marcello La Rosa, Alberto Credi, Serena Silvi
Among the plethora of photochromes reported so far, azobenzene has been proven to be the most suitable photoswitch for molecular systems and materials, due to its highly efficient and clean E-Z photoisomerization. Here we report two ammonium-based molecular axles bearing one or two p-cyanoazobenzene units at the extremities, able to form pseudorotaxanes with a crown ether macrocycle. The photochemistry of these compounds was studied in the isolated forms and in the pseudorotaxanes, showing that the functionalization speeds up the threading process without affecting the photochemical properties of the system...
May 3, 2018: Photochemical & Photobiological Sciences
Juanjuan Li, Xuan Meng, Deng Jian, Di Lu, Xin Zhang, Yanrui Chen, Jundong Zhu, Aiping Fan, Dan Ding, Deling Kong, Zheng Wang, Yanjun Zhao
Nanoparticulate anti-tumor photodynamic therapy (PDT) has been suffering from the limited dose accumulation in tumor. Herein, we report dually hypoxia- and singlet oxygen-responsive polymeric micelles to efficiently utilize the photosensitizer deposited in the disease site and hence facilely improve the therapeutic efficacy of PDT. Tailored methoxy poly(ethylene glycol)-azobenzene-poly(aspartic acid-imidazole) copolymer conjugate was synthesized. The self-assembled conjugate micelles (189 ± 19 nm) could efficiently load a model photosensitizer, chlorin e6 (Ce6) with a loading of 4...
May 3, 2018: ACS Applied Materials & Interfaces
Zili Li, Miao Tang, Chen Jiang, Ruke Bai, Wei Bai
2D polymer sheets containing azobenzene are successfully prepared by a facile strategy of "2D self-assembly polymerization (2DSP)" via free radical polymerization in solution. A bola amphiphile containing azobenzene as a novel monomer is designed and synthesized. The results indicate that single-layer covalent pseudo-2D polymers on a micrometer scale are obtained after polymerization with vinyl monomers. Moreover, the 2D polymer sheets are highly sensitive to UV light due to incorporation of azobenzene groups into the polymer...
May 2, 2018: Macromolecular Rapid Communications
Dipak Samanta, Julius Gemen, Zonglin Chu, Yael Diskin-Posner, Linda J W Shimon, Rafal Klajn
Efficient molecular switching in confined spaces is critical for the successful development of artificial molecular machines. However, molecular switching events often entail large structural changes and therefore require conformational freedom, which is typically limited under confinement conditions. Here, we investigated the behavior of azobenzene-the key building block of light-controlled molecular machines-in a confined environment that is flexible and can adapt its shape to that of the bound guest. To this end, we encapsulated several structurally diverse azobenzenes within the cavity of a flexible, water-soluble coordination cage, and investigated their light-responsive behavior...
May 1, 2018: Proceedings of the National Academy of Sciences of the United States of America
Nicholas Swanson, Ribal Georges Sabat
Non-uniform surface relief diffraction gratings were laser-inscribed on azobenzene molecular glass thin films using a modified Lloyd's mirror interferometer. The azobenzene films were exposed to an adjustable interference pattern produced by the recombination of collimated and spherically divergent laser wave fronts. The localized pitch, grating vector orientation and depth of the resulting non-uniform gratings were measured using an atomic force microscope and a theoretical model was analytically developed to explain the experimental results...
April 2, 2018: Optics Express
Eduard Stadler, Anna Eibel, David Fast, Hilde Freißmuth, Christian Holly, Mathias Wiech, Norbert Moszner, Georg Gescheidt
We have developed a simple method for determining the quantum yields of photo-induced reactions. Our setup features a fibre coupled UV-Vis spectrometer, LED irradiation sources, and a calibrated spectrophotometer for precise measurements of the LED photon flux. The initial slope in time-resolved absorbance profiles provides the quantum yield. We show the feasibility of our methodology for the kinetic analysis of photochemical reactions and quantum yield determination. The typical chemical actinometers, ferrioxalate and ortho-nitrobenzaldehyde, as well as riboflavin, a spiro-compound, phosphorus- and germanium-based photoinitiators for radical polymerizations and the frequently utilized photo-switch azobenzene serve as paradigms...
May 1, 2018: Photochemical & Photobiological Sciences
Ziyao Lyu, Changshun Wang, Yujia Pan, Yifei Yang, Renjie Xia
Polarization modulation was achieved by means of a new type of grating recorded with two 532 nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged...
April 20, 2018: Applied Optics
A Yu Rotov, L A Astakhova, V S Sitnikova, A A Evdokimov, V M Boitsov, M V Dubina, M N Ryazantsev, M L Firsov
Application of molecular photochromic ion channel blockers to recover the visual function of a degenerated retina is one of the promising trends in photopharmacology. To this day, several photochromic azobenzene-based compounds have been proposed and their functionality has been demonstrated on cell lines and knockout mouse models. Further advance necessitates testing of the physiological activity of a great number of new compounds. The goal of this study is to propose animal models of photoreceptor degeneration that are easier to obtain than knockout mouse models but include the main features required for testing the physiological activity of molecular photoswitches...
January 2018: Acta Naturae
Mijanur Rahaman Molla, Poornima Rangadurai, Lucas Antony, Subramani Swaminathan, Juan J de Pablo, S Thayumanavan
Nature has engineered exquisitely responsive systems where molecular-scale information is transferred across an interface and propagated over long length scales. Such systems rely on multiple interacting, signalling and adaptable molecular and supramolecular networks that are built on dynamic, non-equilibrium structures. Comparable synthetic systems are still in their infancy. Here, we demonstrate that the light-induced actuation of a molecularly thin interfacial layer, assembled from a hydrophilic- azobenzene -hydrophobic diblock copolymer, can result in a reversible, long-lived perturbation of a robust glassy membrane across a range of over 500 chemical bonds...
April 30, 2018: Nature Chemistry
Jiandong Guo, Yu Lu, Ruihua Zhao, Zheyuan Liu, Wasihun Menberu, Zhi-Xiang Wang
Titanium catalysis generally prefers redox-neutral mechanisms. Yet it has been reported that titanium could promote bond formations in a way similar to reductive elimination. Accordingly, redox catalytic cycles involving TiIV /TiII cycling have been considered. By studying, as an example, the carboamination of alkynes with alkenes and azobenzene catalyzed by the [TiIV ]=NPh imido complex, we performed DFT computations to gain an understanding of how the "abnormal" catalysis takes place, thereby allowing us to clarify whether the catalysis really follows TiIV /TiII redox mechanisms...
April 30, 2018: Chemistry: a European Journal
Ra-Young Choi, Chang-Hee Lee, Chul-Ho Jun
A methallylsilane coupling reagent, containing both a N-hydroxysuccinimidyl(NHS)-ester group and a UV/vis absorbing azobenzene linker undergoes acid-catalyzed immobilization on silica. Analysis of the UV/vis absorption band associated with the azobenzene group in the adduct enables facile quantitative determination of the extent of loading of the NHS groups. Reaction of NHS-groups on the silica surface with amine groups of GOx and rhodamine can be employed to generate enzyme or dye-immobilized silica for quantitative analysis...
April 30, 2018: Organic Letters
Francesca Cardano, Marco Frasconi, Silvia Giordani
Photo-responsive multifunctional nanomaterials are receiving considerable attention for biological applications because of their unique properties. The functionalization of the surface of carbon nanotubes (CNTs) and graphene, among other carbon based nanomaterials, with molecular switches that exhibit reversible transformations between two or more isomers in response to different kind of external stimuli, such as electromagnetic radiation, temperature and pH, has allowed the control of the optical and electrical properties of the nanomaterial...
2018: Frontiers in Chemistry
Fatemeh Parsa, Massomeh Ghorbanloo, Mohammad Yaser Masoomi, Ali Morsali, Peter C Junk, Jun Wang
Azobenzene groups are widely known as photochromic ligands thus are particularly interesting building blocks for designing receptors for neutral or charged guests. A new metal-organic framework, [Co3 (adc)3 (DMF)4 ].2DMF (compound 1) (adc = azobenzene-4,4-dicarboxylic acid, DMF = N,N-dimethylformamide), was synthesized by solvothermal methods and structurally characterized using X-ray crystallography and a range of spectroscopic techniques. Also, nanorods of compound 1 have been synthesized by a sonochemical process and characterized by field emission scanning electron microscopy (FE-SEM) and powder X-ray diffraction (PXRD)...
July 2018: Ultrasonics Sonochemistry
Zhiyong Li, Xiaoqing Yuan, Ying Feng, Yongkui Chen, Yuling Zhao, Huiyong Wang, Qingli Xu, Jianji Wang
Photo-induced conductivity modulation of stimuli-responsive materials is of great importance from the viewpoint of fundamental research and technology. In this work, 5 new kinds of azobenzene-based photo-responsive ionic liquids were synthesized and characterized, and UV/vis light modulation of their conductivity was investigated in an aqueous solution. The factors affecting the conductivity modulation of the photo-responsive fluids, such as photo-isomerization efficiency, photo-regulation aggregation, concentration and chemical structure of the ionic liquids, were examined systematically...
April 27, 2018: Physical Chemistry Chemical Physics: PCCP
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